An experimentally validated criterion for skim milk powder deposition on stainless steel surfaces

• A novel criterion describing the adhesion of amorphous particles is derived.
• The deposition criterion is experimentally validated for skim milk powder.
• The deposition criterion may be applied in CFD to predict deposition.

Predicting the deposition during the production of milk powder has been identified as a possible avenue to creating new designs and selecting processing conditions that minimise particle deposition. Numerous studies have looked at characterising various aspects of milk powder deposition, agglomeration and caking. Present literature lacks a fundamental and validated criterion that describes the deposition of skim milk powder particle (SMP) impacts with short contact times (<1 s). In this paper standard solutions to the contact mechanics problem of a spherical elastic particle with an adhesive surface impacting a rigid plate at normal and oblique angles form the basis of a derivation of a semi-empirical criterion that describes whether a particle sticks after impacting a wall. To validate the criterion, the determining factors of skim milk powder deposition, which are air temperature, water activity (i.e. relative humidity), plate (or wall) temperature, and particle size, velocity and impact angle, are isolated and experimentally tested using the Particle Gun technique.